1. Field of the Invention
This field of the invention relates generally to a class of devices and integration of an array of these devices into a system for switching optical signals. In particular, the devices are made with materials and processes that are compatible with the prevalent semiconductor manufacturing practice, hence capable of producing products in high volume and low cost.
2. Background
The interest in these devices has been driven by the tremendous increase in demand for more usage and faster communications systems, i.e. greater bandwidth, in the telecommunication industry. The prime examples of applications that are pushing this demand are the Internet, video/music on demand, and corporate data storage. The existing telecommunication infrastructure, which was largely developed for telephone calls, is now incapable of meeting the demands for new applications of data communication.
Several options have been developed to meet this new demand. These options include wireless, optical, and free-space laser communication technologies. To date, the most promising technology capable of meeting the projected bandwidth requirements of the future is the optical technology.
In an all optical network, or in a combination of an optical and electrical network, the necessary components include a signal carrier medium (i.e. optical fiber), signal routing systems, and data control systems. These signal routing systems have devices which switch optical signals between optical fibers.
In the prior art approaches, the switching of optical signals can be accomplished in predominantly two major approaches: electrical and optical. Today, most systems use electrical switching. In these systems, at the network junctions, the optical signals must first be converted into electrical signals. The converted electrical signals are then switched to the designated channel by integrated circuits. Lastly, the electrical signals must be converted back into optical signals before the signals can be passed onto the optical fiber toward the next destination. Such optical converters are relatively expensive compared to the rest of the transmission equipment.
Electrical switching technology is reliable, inexpensive (except for optical converters), and permits signal reconditioning and monitoring. The main drawback with electrical switching systems is that the number of junctions in a long distance network can be large, and the total cost of converters is very high. Furthermore, typically more than 70% of signals arriving at a junction require only simple straight pass-through, and conversion (down and up conversions) of the full signal results in inefficient use of hardware. System designers also anticipate that future systems are best served by transparent optical switch capabilities; that is, switching systems capable of redirecting the path of the optical signal without regard to the bit rate, data format, or wavelength of the optical signal between the input and output ports. Most electrical switching systems are designed for a specific rate and format, and cannot accommodate multiple and dynamic rates and formats. Future systems will also be required to handle optical signals of different wavelengths, which in an electrical switching network would necessitate the use of separate channels for each wavelength. These limitations of the electrical switching system provide new opportunities for the development of improved optical switching systems.
A switch that directly affects the direction of light path is often referred to as an Optical Cross Connect (OXC). Conventional optical fabrication techniques using glass and other optical substrates cannot generate products that meet the performance and cost requirements for data communication applications. Unlike the electrical switching technique that is based on matured integrated circuit technology, optical switching (ones that can achieve high port count) depends on technologies that are relatively new. The use of micromachining is one such new approach. The term MEMS (Micro Electro-Mechanical Systems) is used to describe devices made using wafer fabrication process by micromachining (mostly on silicon wafers). The batch processing capabilities of MEMS enable the production of these devices at low cost and in large volume.
MEMS-based optical switches can be largely grouped into three categories: 1) silicon mirrors, 2) fluid switches, and 3) thermal-optical switches. Both fluid and thermal-optical switches have been demonstrated, but these technologies lack the ability to scale up to a high number of channels or port counts. A high port count is important to switch a large number of fibers efficiently at the junctions. Thus far, the use of silicon mirrors in a three dimensional (3D) space is the only approach where a high port count (e.g., greater than 1000) is achievable.
Optical Cross Connects that use 3D silicon mirrors face extreme challenges. These systems require very tight angular control of the beam path and a large free space distance between reflective mirrors in order to create a device with high port counts. The precise angular controls required are typically not achievable without an active control of beam paths. Since each path has to be monitored and steered, the resulting system can be complex and costly. These systems also require substantial software and electrical (processing) power to monitor and control the position of each mirror. Since the mirror can be moved in two directions through an infinite number of possible positions (i.e., analog motion), the resulting feedback acquisition and control system can be very complex, particularly for a switch having large port counts. For example, as described in a recent development report, Lucent Technology""s relatively small 3D mirror-switching prototype was accompanied by support equipment that occupied three full-size cabinets of control electronics.
Ideally, an optical switch will have the following principal characteristics:
1) Be scalable to accommodate large port counts ( greater than 1000 ports);
2) Be reliable;
3) Be built at a low cost;
4) Have a low switching time;
5) Have a low insertion loss/cross talk.
While the 3D-silicon mirror can meet the scalability requirement, it cannot achieve the rest of the objectives. Therefore, there is a need for a new approach whereby the complex nature of the 3D free space optical paths and analog control can be replaced with guided optical paths and digital (two states) switching. Such a system will greatly simplify the operation of switching, enhance reliability and performance, while significantly lowering cost. The disclosure in the following sections describes such a system.
The invention relates to a method and apparatus for switching optical signals using a movable optically transmissive microstructure. This apparatus uses movable microstructures to direct multiple optical paths.
A first, separate aspect of the invention is an apparatus for switching optical signals by selectively moving a movable optically transmissive microstructure, where the optical signals take one set of paths if the microstructure is not moved and the optical signals take a different set of paths if the microstructure is moved.
A second, separate aspect of the invention is an apparatus for switching optical signals by selectively moving a movable optically transmissive microstructure, where the optical path that the optical signals take depends on the position of the microstructure.
A third, separate aspect of the invention is an apparatus for switching optical signals comprising a fixed input waveguide, at least two optically transmissive waveguides mounted to a movable microstructure, and a fixed output waveguide.
A fourth, separate aspect of the invention is an apparatus for switching optical signals comprising a movable optically transmissive microstructure having an input and an output, where the input is positioned in close proximity (e.g., a small air gap) to a waveguide containing an incoming optical signal and the output is positioned in close proximity (e.g., a small air gap) to a waveguide for carrying an outgoing optical signal.
A fifth, separate aspect of the invention is an apparatus for switching optical signals comprising a microstructure mounted for movement relative to the substrate of a silicon chip, the microstructure carrying optically transmissive waveguides.
A sixth, separate aspect of the invention is an apparatus for switching optical signals comprising a substrate of a chip, a microstructure carrying optically transmissive waveguides and movably mounted to the substrate for movement relative to the substrate, and a control structure for moving the microstructure relative to the substrate.
A seventh, separate aspect of the invention is an apparatus for switching optical signals comprising a substrate of a chip, a support structure mounted to the substrate, a microstructure carrying optically transmissive waveguides and movably mounted to the support structure for movement relative to the substrate, and a control structure for moving the microstructure relative to the substrate.
An eighth, separate aspect of the invention is an apparatus for switching optical signals comprising an optical switch having a movable optically transmissive microstructure that switches optical signals in the X-Y dimension and an optical switch having a movable optically transmissive microstructure that switches optical signals in the Z dimension, thereby providing the capability to switch optical signals in 3 dimensions.
A ninth, separate aspect of the invention is an apparatus for switching optical signals comprising a micro-switch element having a movable optically transmissive microstructure, the micro-switch element being capable of directing optical signals from two inputs to any of two outputs.
A tenth, separate aspect of the invention is an apparatus for switching optical signals comprising a movable optically transmissive microstructure which corrects optical misalignment from a two dimensional array of optical outputs by using a two dimensional array of optic elements placed at the interface.
An eleventh, separate aspect of the invention is a method of switching optical signals comprising the step of selectively moving a movable optically transmissive microstructure, where the optical signals take one set of paths if the microstructure is not moved and the optical signals take a different set of paths if the microstructure is moved.
A twelfth, separate aspect of the invention is a method of switching optical signals comprising the steps of providing an incoming optical signal through a fixed input waveguide, selectively directing the optical signal into one of at least two waveguides mounted to a movable microstructure by selectively moving the microstructure, and outputting the optical signal through a fixed output waveguide.
A thirteenth, separate aspect of the invention is a method of switching optical signals comprising the step of positioning a movable optically transmissive microstructure having an input and an output such that the input is positioned in close proximity (e.g., a small air gap) to a waveguide containing an incoming optical signal and the output is positioned in close proximity (e.g., a small air gap) to a waveguide for carrying an outgoing optical signal.
A fourteenth, separate aspect of the invention is a method of switching optical signals comprising the step of mounting an optically transmissive microstructure for movement relative to the substrate of a silicon chip, the microstructure carrying optically transmissive waveguides.
A fifteenth, separate aspect of the invention is a method of switching optical signals comprising the steps of providing a substrate of a chip, movably mounting a microstructure carrying optically transmissive waveguides to the substrate for movement relative to the substrate, and selectively moving the microstructure relative to the substrate to switch the optical signals.
A sixteenth, separate aspect of the invention is a method of switching optical signals comprising the steps of providing a support structure mounted to the substrate of a chip, movably mounting a microstructure carrying optically transmissive waveguides to the support structure for movement relative to the substrate, and selectively moving the microstructure relative to the substrate to switch the optical signals.
A seventeenth, separate aspect of the invention is a method of switching optical signals comprising the steps of providing an optical switch that switches optical signals in the X-Y dimension and providing an optical switch that switches optical signals in the Z dimension, thereby providing the capability to switch optical signals in 3 dimensions.
An eighteenth, separate aspect of the invention is a method of switching optical signals comprising the steps of providing a micro-switch element having a movable optically transmissive microstructure capable of directing optical signals from two inputs to any of two outputs.
A nineteenth, separate aspect of the invention is a method of switching optical signals comprising the steps of selectively moving an optically transmissive microstructure to switch optical signals and correcting optical misalignment from a two dimensional array of optical outputs by using a two dimensional array of optic elements placed at the interface.
A twentieth, separate aspect of the invention is a method of fabricating movable and stationary waveguides using a movable optically transmissive microstructure.
A twenty-first, separate aspect of the invention is a method of fabricating movable and stationary waveguides using a movable optically transmissive microstructure, the method comprising the steps of integrating simple switch elements and forming a structure capable of simultaneously switching a high density of optical signals from a two dimensional input array to a two dimensional output array.
A twenty-second, separate aspect of the invention is any of the above separate aspects, either individually or in some combination.
Further separate aspects of the invention can also be found in a system or method that practices any of the above separate aspects, either individually or in some combination.
Other systems, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims.